A Tweet to Kurt Eichenwald, a Strobe and a Seizure. Now, an Arrest.

WASHINGTON — When the journalist Kurt Eichenwald opened an animated image sent to him on Twitter in December, the message “You deserve a seizure for your posts” appeared in capital letters along with a blinding strobe light. Mr. Eichenwald, who has epilepsy, immediately suffered a seizure.

On Friday, the Federal Bureau of Investigation said it had arrested John Rayne Rivello, 29, at his home in Salisbury, Md., and accused him of sending the electronic file. The agency charged Mr. Rivello with criminal cyberstalking with the intent to kill or cause bodily harm.

The charge could carry a prison sentence of up to 10 years, according to the United States district attorney in Dallas, who is prosecuting the case.

The unusual case has shown how online tools can be deployed as weapons capable of physical harm. The F.B.I. and the Dallas police led the investigation into Mr. Rivello, and the police said he sent the strobe light knowing that it was likely to lead Mr. Eichenwald, who has publicly discussed his epilepsy, into a seizure.

Steven Lieberman, Mr. Eichenwald’s lawyer, has argued that the use of the strobe light in a GIF, or moving graphic, was akin to sending an explosive or poison in the mail.

“This electronic message was no different than a bomb sent in the mail or anthrax sent in an envelope,” said Mr. Lieberman, who is working on the case as a pro bono service. “It triggers a physical effect.” (Mr. Lieberman represents The New York Times as outside counsel, and Mr. Eichenwald was a reporter for The Times from 1986 to 2006.)

That comparison makes Mr. Eichenwald’s case different from other claims of harmful attacks using social media. Lawsuits involving stalking and bullying on the internet have focused on how online content, such as disparaging and abusive messages and pictures, can harm victims emotionally and even increase the risk of suicide. But with this case, Mr. Rivello is said to have designed the attack specifically around the victim’s medical condition.

“This is an interesting and unique case in that there are lots of online attacks that can have physical consequences, such as an attack on an electrical grid or the control of air traffic control,” said Vivek Krishnamurthy, an assistant director at the Cyberlaw Clinic at Harvard Law School. “But this is distinguishable because it is a targeted physical attack that was personal, using a plain-Jane tool.”

Investigators found evidence of the plan to attack Mr. Eichenwald from a search of Mr. Rivello’s Twitter account, the Justice Department said in a statement. After obtaining a search warrant for Mr. Rivello’s social media account, investigators found direct messages to other Twitter users about Mr. Eichenwald, including one that read, “I hope this sends him into a seizure.”

Other Twitter messages from Mr. Rivello included one that read, “I know he has epilepsy.”

Investigators also searched one of Mr. Rivello’s digital accounts and found a screenshot of Mr. Eichenwald’s Wikipedia page that had been altered to show a fake date of death of Dec. 16, 2016, the day after the strobe light attack, the Justice Department said. The digital account also contained screenshots from epilepsy.com with a list of commonly reported epilepsy seizure triggers.

Mr. Eichenwald, 55, who has about 318,000 followers on Twitter and has written four books, including “The Informant,” had been critical of Donald J. Trump throughout his presidential campaign. Mr. Eichenwald suspected that the attacker, who operated under the pseudonym “@jew_goldstein” on Twitter, was a supporter of Mr. Trump. Twitter has since suspended the account.

Late in the evening on Dec. 15, Mr. Eichenwald went to his home office in Dallas and saw that @jew_goldstein had replied to a Twitter post with a GIF. When Mr. Eichenwald clicked on the file, the strobe light triggered the seizure, his lawyer said. Mr. Eichenwald fell to the ground.

His wife, Theresa, found him on the floor and saw the Twitter post on his computer screen. She called 911 and then replied on Twitter: “@jew_goldstein This is his wife, you caused a seizure. I have your information and have called the police to report the assault.”

Mr. Eichenwald was incapacitated for several days, lost feeling in his left hand and had trouble speaking for several weeks, according to his lawyer.

Soon after, he contacted the Dallas district attorney’s office. In state court, Mr. Eichenwald’s lawyer filed for permission to serve a subpoena of Twitter to gain access to the account for @jew_goldstein. The social media company indicated it would cooperate, which drew protest from an anonymous “John Doe” filing that was intended to quash the subpoena.

Investigators would not say how they tracked down Mr. Rivello. Court documents were not immediately available. Mr. Rivello will be transferred to Dallas, where Mr. Eichenwald lives, to appear before the District Court for the Northern District of Texas.

Mr. Eichenwald used Twitter on Friday to thank officials for their work on his case. He said that since the Dec. 15 message, 40 more accounts have sent him strobe light images.

“Details of their cases are with the FBI. Stop sending them,” he wrote on Twitter.

A version of this article appears in print on , on Page B2 of the New York edition with the headline: A Tweet Causes a Seizure, and a Suspect Is Charged With Cyberstalking. Order Reprints | Today’s Paper | Subscribe